1. Field of the Invention
The present invention relates to a solid-state image pickup device, a method for driving a solid-state image pickup device, and an image pickup apparatus.
2. Description of the Related Art
Typically, a solid-state image pickup device has a region having pixels, which are shielded from light, for outputting black reference signals (hereinafter, referred to as an “optical black pixel region”) that is disposed around a region having effective pixels for providing signals which are eventually to be used as image signals (hereinafter, referred to as an effective pixel region).
In the solid-state image pickup device having the optical black pixel region, a layout of an upper layer of a light-shielding layer of a light-shielding portion of the optical black pixel region is different from a layout of the upper layer of the light-shielding layer of an opening portion of the effective pixel region. Accordingly, a film thickness of the upper layer of the light-shielding layer of a central portion of the effective pixel region is different from a film thickness of the upper layer of the light-shielding layer of a boundary portion between the effective pixel region and the optical black pixel region. Examples of the upper layer of the light-shielding layer include a passivation film, a color filter, a lens member, and so forth.
Because the difference in the film thickness of the upper layer of the light-shielding layer influences the optical characteristics, optical non-uniformity occurs in a peripheral portion of the effective pixel region. Furthermore, because of the difference between a shape of a light-shielding metal of the opening portion of the effective pixel region and a shape of the light-shielding metal of the optical black pixel region, variation in supplying of a hydrogen group from a passivation film to a silicon interface occurs. The interface state varies at the end of the silicon interface, and variation in dark current or random noise occurs.
In order to prevent the above-mentioned problems from occurring, hitherto, a configuration has been used: in which dummy pixels are disposed in the boundary portion between the optical black pixel region and the effective pixel region, i.e., a region in which the film thickness of the upper layer of the light-shielding layer differs; and in which signals of the dummy pixels are not used as image signals. Furthermore, in a charge coupled device (CCD) solid-state image pickup device, only when a frame interline scheme is employed, a configuration has been used: in which charge of dummy pixels that are provided at the top and bottom sides of an effective pixel region is drained into the outside of a horizontal transfer section, thereby reducing increase in transfer frequency (see Japanese Patent No. 3321787).